1.1 The present invention is related to a starter for starting an internal combustion engine. More precisely, the present invention is based on a starter comprising a starter motor for generating a torque for rotating a crankshaft of the engine and a shift motor for connecting and disconnecting the starter motor to the crankshaft. The present invention is intended to compactize the starter while realizing a quick, smooth and reliable operation of the starter.
1.2 Prior Arts
Conventional starter is typically constructed and operated as follows.
A shaft of a starter motor extrudes from a motor body and a pinion gear is splined to the shaft through a one-way transmission mechanism so as to slide along the shaft and rotate uni-directionally. The pinion gear engages meshingly with a ring gear which is connected to an engine when the pinion gear is at a geared position. When the pinion gear is at a detached position, the pinion gear is detached from the ring gear. The one-way transmission mechanism transmits rotation of the starter motor to the engine but does not transmit rotation of the engine to the starter motor.
Position of the pinion gear is shifted selectively by means of a shifting arm which is activated by a magnetic switch and a plunger connecting them together.
In such a case, driving force shifting the pinion gear varies according to the position of the pinion gear because of a geometrical feature of the magnetic switch, and the shift arm often thrusts the pinion gear to come in contact with the ring gear strikingly. The gears are apt to be damaged, consequently. Further, relatively large electric current is required for activating the magnetic switch.
In order to avoid above-mentioned inconvenience, there are another type of starters which are provided with a shifting motor instead of the magnetic switch for activating the shift arm, an example is disclosed by Japanese Utility Model Application laid open with No. 60-30364. In the invention, a shifting motor comprises a shifting motor shaft extruding out of a motor body and spline cogs are formed in the shaft. A slider gears into the cogs of the shaft so that it moves along the shaft according to a rotation of the shaft. The slider holds an end of a shift arm, the other end of which being connected to the pinion gear for shifting the latter according to a rotational movement of the shifting motor.
A problem as to this starter is that a reaction force which is not parallel to the shifting motor shaft is exerted to the shaft by the shift arm, consequently, a bending moment is exerted to the shaft obstructing a smooth rotation of the shaft and the shifting motor. As a result, a larger shifting motor is needed to overcome the reaction force. The situation is improved when a distal end of the shifting motor shaft is supported by a bearing means such as a roller bearing. In the case, the non-axial reaction force is received both by the shifting motor and the bearing. Therefore, the reaction force exerted to the motor is reduced by half. But the abovementioned construction is not still enough to reduce drastically the non-axial force acting on the shaft of the shifting motor. As a result, shifting action is not smooth, quick, or certain. Furthermore, the shifting motor and an electric supply system for the motor become large in order to secure a necessary driving force.